On Thu, Oct 17, 2013 at 3:39 PM, Brad Neuhauser
<<mailto:brad.neuhau...@gmail.com>brad.neuhau...@gmail.com> wrote:
From
<http://en.wikipedia.org/wiki/Interstate_Highway_System#Primary_.28one-_and_two-digit.29_routes_.28contiguous_U.S..29>http://en.wikipedia.org/wiki/Interstate_Highway_System#Primary_.28one-_and_two-digit.29_routes_.28contiguous_U.S..29
:
"In the numbering scheme, east-west highways are assigned even
numbers and north-south highways are assigned odd numbers. Odd route
numbers increase from west to east, and even-numbered routes
increase from south to north (to avoid confusion with the U.S.
Highways, which increase from east to west and north to south),
though there are exceptions to both principles in several locations."
Field signage is sometimes inconsistent with the official rules; for
example, US 68 is mostly (entirely?) signed north-south, and I-69
becomes east-west between Lansing and Port Huron. States may have
their own rules; some states (MS, FL) follow the even-odd rules that
the national routes do, some use an opposite pattern (even N-S, odd
E-W), and some have no pattern at all (GA, TN).
There are also cases of signage by loop nesting ("inner"
clockwise/"outer" counterclockwise for RHD) - I-495 around
Washington and I-440 around Raleigh NC are examples, along with GA
10 Loop around Athens GA. And in Canada the QEW is "directionally"
signed by destination (Toronto on the clockwise carriageway, Niagara
and then Fort Erie on the counterclockwise one). There may be a few
more oddballs I've missed.
IMO preferred practice should be a relation for each continuous
cardinal direction, to keep validation simple; undivided roads
should use forward/backward roles to distinguish which relation
applies to the underlying way's forward/backward traversal. It
shouldn't be too terribly hard to come up with an algorithm to fixup
the existing single-relation cases, particularly for the ones where
the routes are entirely dual carriageway, although occasionally the
heuristics will be wrong and need a manual edit.
Well said, Chris. +1, lands right in the middle of where it might, imho.
Manual edits on exceptional cases means that somebody, somewhere is
paying attention. In a big set, with careful management, that's to
be expected. Good show.
Encore, author. This is a serious project which aims to accurately
map "what is." Nice job so far, everybody. I very much like this
crowd-sourced map. It only keeps getting better and better.
SteveA
California
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